fix(Comment): Initialize childrenCount as integer

[provokateurin]

#47984

Summary

Expected to be an integer:

server/lib/private/Comments/Comment.php

Lines 138 to 140 in 01478f1

	public function getChildrenCount(): int {
	return $this->data['childrenCount'];
	}

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

/backport to stable30

[provokateurin]

/backport to stable29

[provokateurin]

/backport to stable28